Fabrication of semiconductor devices



June 19, 1962 J. A. SWARTZMAN 3,

FABRICATION OF SEMICONDUCTOR DEVICES Filed Jan. 16, 1959 3 Sheets-Sheet 1 June 19, 1962 Y J. A. SWARTZMAN FABRICATION OF SEMICONDUCTOR DEVICES Filed Jan. 16, 1959 FIQAZ.

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June 19, 1962 J. A. SWARTZMAN 3,039,514

FABRICATION OF SEMICONDUCTOR DEVICES Filed Jan. 16, 1959 3 Sheets-Sheet 3 United States Patent 3,039,514 FABRICATION 0F SEMICONDUCTOR DEVICES Joseph A. Swartzman, Levittown, Pa., assignor, by mesne assignments, to Philco Corporation, Philadelphia, Pa., a corporation of Delaware Filed Jan. 16, 1959, Ser. No. 787,303 2 Claims. (Cl. 156-345) This invention relates to the fabrication of semiconductor devices, for example transistors, and has to do particularly with the formation of electrode elements on semiconductor blanks by jet etching and jet plating operations.

It has been discovered that the jet etching as well as the jet plating of the semiconductor can be improved by a new type of pneumatic treatment, applied to the etching or plating zone, and it is a basic object of the invention to provide a method of and means for such improved etching or plating.

Although great advance has been made in applying various jet etching and jet plating operations in the field of semiconductor fabrication, and although some of the newer jet operations have been combined with pneumatic treatment of the jet region, further improvement has been found possible, particularly as to maintenance of uniform conditions of treatment. It has also been found that improvement is possible by the use of a pneumatic current which maintains uniformity of re moval of jet liquid from all parts of the etching or plating zone. It is therefore a specific object of the invention to provide mean-s for, and a method of, maintaining uniformity of jet etching or plating conditions and of jet liquid removal.

Another specific object of the invention is eifectively to protect equipment as well as personnel from harmful elfects of chemically aggressive fluids, constituting or surrounding the jet.

Briefly described, the new apparatus utilizes suitable means for directing a liquid jet against an etching or plating zone constituting part of a surface of a semiconductor blank, thereby forming a sheet of liquid flowing outwardly away from said zone; and in accordance with the invention the new apparatus provides means for passing a current of gas across the peripheral edge of said flowing sheet, in such a way that liquid is entrained by said current of gas and withdrawn from said sheet in form of drops directed away from said zone. For the purpose of so directing the liquid, in an efficient way, it has been found particularly desirable to pass said current of gas across the edge of said liquid sheet as a positively directed current having a velocity just about sufficient to entrain the liquid drops.

The nature and advantages of the invention will appear more clearly from consideration of preferred embodiments, which will now be described with reference to the drawing.

FIGURE 1 is a side view of apparatus incorporating the invention. The same apparatus is shown in FIG- URE 2, in a view taken along line 2-2 in FIGURE 1. FIGURES 3 and 4 are respectively an enlarged detail view of apparatus shown in FIGURE 2 and a view thereof taken along line 4-4 in FIGURE 3. FIGURE 5 is a view similar to FIGURE 1 but showing a modified embodiment of the invention. FIGURE 6 is an enlarged, fragmentary view of another modified embodiment of the invention, shown in detail similar to FIG- URE 3; and FIGURE 7 is an additionally enlarged view taken along line 77 in FIGURE 6.

Referring to FIGURE 1, suction nozzle or housing 10, mounted on holder 11, is connected with suction lead 12 of air-pump 13, said pump discharging at 14 into reservoir 15 for jet liquid 16. Such liquid is with- 3,039,514 Patented June 19, 1962 drawn from the reservoir by suction lead 17 of liquid pump 18, the discharge lead 19 of the latter pump being connected with jet nozzle 20, mounted on holder 21. Nozzles 10, 20 are made of chemically inert material, for instance of glass or the like. The pumps are shown schematically and on a reduced scale, whereas the actual sizes of nozzles 10 and 20, in illustrative embodiments of the invention, approximately coincide with the respective dimensions used in FIGURES 1 and 2.

As shown in the latter figure, semiconductor holder 22 reaches from a position adjacent suction nozzle or housing 10 into the interior of said nozzle or housing, to hold semiconductor blank 23 freely supported therein. For this purpose an elongate transistor tab 24 is held by holder 22, and transistor blank 23 is mounted on this tab, as is best shown in FIGURES 3 and 4. Preferably, suction nozzle 10 is transparent and the inside thereof is illuminated by light beams 25, 26 (FIGURES l and 3), provided by suitable light Sources.

As shown in FIGURE 3, a liquid jet 27 is formed by a suitable liquid discharge aperture 28 in jet nozzle 7 20, and the jet is introduced, through aperture 29 of aspirator nozzle 10, into suction zone 30 within the latter nozzle, the jet being shown as directed against impact area 31 on top surface 32 of blank 23. Etching or plating is achieved in this impact area, by virtue of generally known chemical or electrochemical characteristics of liquid 16, with or without the aid of further equipment such as an electrode, not shown, in liquid 16.

The area of inlet aperture 29 desirably equals several times that of discharge aperture 28 and jet 27, for instance, the respective diameters may be 3.0 mm. and 1.0 mm. The approximate size of the etching or plating zone, or impact area, may then be of the order of about 1.3 or 1.5 mm. Transistor 23 may be a square body of about 5 mm. side length. Such dimensions of course are stated merely for illustrative purposes.

As further shown in FIGURES 3 and 4, the liquid coming from jet 27 moves away from impact area 31 in form of a substantially circular, thin, generally planar, outwardly flowing liquid sheet 33, the liquid being outwardly impelled by such kinetic energy as has been provided by liquid pump 18 and not as yet dissipated. This flowing liquid sheet has an approximately round circumference 34 concentric with area 31 and further has, adjacent said circumference, a relatively thick liquid ring 35, which ring may be said to constitute a zone of drops 36 in state of formation due to the cohesion of surface tension of the liquid.

It has been found to be necessary, for goo-d and consistent results of jet etching and jet plating operations, to control such drop formation with great care, in or adjacent liquid ring 35, "and thereby to enhance uniformity of conditions prevailing in jet impact area 31.

For this purpose it is necessary in the first place to make the inside of ring 35 substantially larger than said impact area 31; in some cases it seems desirable to make it even larger than the entire blank 23. For instance if zone 30 has a clear width of 15 mm., ring 35 may be given a diameter almost or about equal to such width, by suitable adjustment of the speed of pump 18. On the inside of such ring, a flat, transparent liquid sheet or window 33 is formed, which in typical applications of the invention has a diameter of about 10 mm. This liquid sheet, being formed by liquid outwardly turning away from the jet column, is thinner than the jet column is wide, as is shown in FIGURE 3. The actual dimensions, shown on the drawing, of course are purely illustrative.

It has further been found that care must be taken to remove liquid from ring 35 in or as a current which maintains window 33 in its position as shown and in uniformly flat, transparent condition. Such current, accordingly, should be strong enough to entrain liquid drops 36 formed at 35, but should also be so controlled and/or directed as to safely avoid driving any liquid into or across impact area 31. This has not been achieved in prior methods and devices, developed for the present field. In many cases, for instance, a current strong enough to entrain liquid drops from the edge of the liquid sheet has tended at times to cause irregular motions of the jet or of drops, thereby destroying uniformity of conditions in the etching or plating zone.

The. new apparatus avoids irregularities of this type by novel means for pneumatic removal of liquid. For this purpose, according to one aspect of the invention, blank 23 is located not between an aspirating nozzle and a jet nozzle, as heretofore, but within aspirating nozzle 1%, that is, between aspirating aperture 29 and suction duct 12. Excellent control over the velocity, direction, and effect of the pneumatic current, passing over the blank, has been achieved by this improvement.

It is preferred that jet 27 be coaxial with aspirating aperture 29, as shown. The aperture is made large enough to allow relatively slow inflow 37 of air and thus to avoid pneumatic disruption of the jet.

It is possible to move the aspirated air in form of a current 38 directed longitudinally of zone 31 and diametrically of window 33, as is most clearly shown in FIGURE 4. While being still slower than the aspirated inflow current 37, this air current 3-8 is nevertheless of substantial velocity. Desirably, said air current is just about rapid enough, over the entire cross-sectional area of zone 30, to entrain the liquid drops 36 into which liquid ring .35 breaks up. When at the same time a rapid outward flow of liquid is ensured, in sheet 33, by suitable operation of liquid pump 18, and when air current 38 within nozzle is suitably adjusted, by proper speed of operation of suction pump 13, the generally longitudinal direction of the air flow seems to induce a peripheral flow of liquid, in and along liquid ring 35. This causes drops 36 to be formed mainly or exclusively in an arcuate breakup area 39, constituting part of ring 35 and disposed between window 33 and suction conduit 12. Such operation, in turn, keeps most or all parts of window 33 undisturbed by liquid drops, wavelets and the like, thereby contributing greatly to the aforesaid, desirable uniformity of operating conditions in impact region 31.

In the absence of such treatment, serious difiiculties have hitherto been encountered in many of the jet etching and jet plating methods, applied to transistor blanks and the like. Some of the (ilfilCUltlCS, as already indicated, were connected with the fact that particles or bodies of liquidoften a liquid of chemically very active naturetended irregularly to accumulate, or to move about, in or adjacent the zone of desired etching or plating. Such liquids, and also vapors thereof, then had the opportunity to act irregularly, not only upon blank 23 but also on adjacent equipment. Even the operators skin or clothes could be harmed. The new pattern of liquid and gas currents, by contrast, makes the fabrication of transistors safe and convenient, as well as considerably more efficient.

The exact fluid flow pattern provided by the invention is dependent not only on operating characteristics of liquid and suction pumps, as has already been indicated but also on the arrangement of walls and apertures of the suction nozzle. As shown in FIGURES 1 and 4, nozzle 10 has a closed end portion 40, While having an aperture 41, for introduction and removal of blank 23, in side wall 42 of the nozzle. Such an aperture 41 desirably has a shape approximately similar to that of said blank, while being slightly larger than the blank and being suitably spaced from end wall 40.

It is, however, possible and in some cases preferable, as

shown in FIGURE 5, to leave the end 50 of an aspirating nozzle or housing 51 open. Such end then forms, with a suitably positioned blank holder 52, a proper suction opening 53 for the suction nozzle. As further shown in this figure, blank 23 can be disposed between a pair of jet inlet openings 54-, 55, associated with a pair of jet nozzles 56, 57, which nozzles can be disposed along a line normal to the axes of nozzle 51 and of blank 23.

It is also possible, as shown in FIGURES 6 and 7, to orient a blank 23 transversely of the axis of a suction nozzle and housing 70; and in such cases the nozzle or housing may be coaxial with the liquid discharge nozzle 71. This arrangement facilitates achievement of fully symmetrical irradiation of a jet impact area 72 by light beams 73, 74 entering around jet 75. Similarly symmetrical illumination 76, 77 may thus be provided also on the underside of blank 23. Additionally, this arrangement facilitates fully symmetrical removal of spent liquid 78 from liquid sheet 79 and ring 80, the air or other gas being so aspirated at 81, and removed at 82, that it flows transversely of blank 23 and liquid sheet 79. In some such cases nozzle 70 may have an enlarged upper end 83, with a notch 84 in the upper edge 85 in order to facilitate introduction and support of tab 24, holding blank 23. A variety of configurations can evidently be used for removal of liquid and gas through an outlet duct 36.

The invention has been found to be useful as applied to a variety of sizes of jet currents and corresponding sizes of the impact area or etching or plating area. In this respect, as well as by other features described and claimed herein, the present invention differs from jet treatment means and methods heretofore applied. In several of said prior methods, pneumatic treatment or aspiration has been applied to a jet and impact area of minute diameter, such as two millimeters or less. The aspiration of air or gas, in such prior applications, served to prevent formation of a single, self-supporting, adherent, chemically or electro-chemically troublesome ball or drop of jet liquid, in and directly around the minute jet impact area. Such drop formation was counteracted by providing at least one pneumatic nozzle, opposite the blank, with an air intake aperture directed toward the blank. The semiconductor blank, accordingly, was disposed between an'aspirator nozzle and a minute jet nozzle. According to the present invention, by contrast, a semiconductor blank is treated within an aspirator nozzle, by a jet of suitable size.

While only three embodiments of the new apparatus and the operation thereof have been described, it should be understood that details of construction and operation of such embodiments are not to be construed as limitative of the invention, except insofar as is consistent with the scope of the following claims.

I claim:

1. Apparatus for etching a semiconductor blank, comprising:

nozzle means for discharging a jet of flowing liquid electrolyte etchant against an impact area on a flat surface of said blank and for thereby impelling the liquid electrolyte outwardly from said impact area along said flat surface as a thin sheet of flowing liquid;

tubular wall structure extending transversely of and closely surrounding said blank and said sheet of liquid and closely spaced from peripheral portions thereof to define a narrow, generally annular passage for a current of gas between said peripheral portions and said tubular wall structure; and

means for passing a current of gas along the inside of said tubular wall structure and through said narrow, generally annular passage to remove liquid from the peripheral portions of said sheet of liquid.

2. Apparatus as described in claim 1 wherein said tubular wall structure has an upwardly extending, up-

References Cited in the file of this patent UNITED STATES PATENTS Henderson Sept. 19, 1950 6 Guenst Sept. 25, 1951 Evers Oct. 16, 1956 Williams July 16, 1957 Derick et a1. Aug. 27, 1957 Topfer Nov. 17, 1959 Vaughan May 17, 1960 Vaughan Dec. 12, 1961 

